The present disclosure relates to electro-photographic printing. More particularly, this disclosure relates to devices that use charged toner particles for the development of an image between conductive elements under the influence of an electric field. In many printing devices the charged particles are of a dry toner, while in others the particles are dispersed in a liquid. One example of the latter is Liquid Toner Electrophotography (LEP), in which the charged toner particles are dispersed in a carrier liquid (hereinafter “liquid toner”). The conductive elements can be part of a Binary Ink Development (BID) unit, which in LEP uses a developer cylinder with a coating of high concentration liquid toner to transfer toner particles onto a photoconductive surface. When the surface of the developer bearing the layer of liquid toner concentrate is engaged with the photoconductive surface of the cylinder, the difference in voltage between the developer cylinder and the photoconductive surface allows for selective transfer of the layer of toner particles to the photoconductive surface, thereby developing the latent image. The methods and apparatus for exposing the photoconductive surface to an image in order to create the latent image are well known to those of skill in the art.
One factor that has an effect on the operation of BID units is the current on the BID electrode(s). Methods have been developed for ink charge monitoring based upon BID current levels. However, different BID units of the same design, using the same ink solution and applying the same set of voltages, can have a different BID electrode current due to manufacturing variations, variations in BID structure, change in electrode material, variations in developer material, developer conductivity and other parameters affecting electrode current. These differences in electrode current can cause a deviation from the desired working point for the BID unit when changing BID units or installing new ones, since the working point for the BID allows correlation of the BID electrode current with the ink charge. When installing a new BID unit, even though the voltage levels remain the same or are set to default values, the BID current can change, potentially causing the ink charge monitoring system to make unnecessary or improper adjustments. This can lead to undesired print quality variations between different printer units of the same design. For example, variations in electrode current can result in undesired variation in ink thickness and ink coverage in a finished print.